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Flying spiders spin a balloon of silk to catch a ride with the wind

June 14 (UPI) — Some spiders take air balloon rides, and researchers at the Technical University of Berlin are trying figure out how.

Species belonging to the Xysticus genus, a group of crab spiders, don’t build webs and spend most of their time on the ground. But they do have the ability to weave silk threads, and several use that ability to take to the air.

According to a new study published this week in the journal PLOS Biology, the medium to large spiders weave silk threads that inflate and take on sail-like shapes as they catch the wind, pulling them into the air.

The abdomen of the crab spider features silk spinnerets with hundreds of spigots, each able to eject silk strands measuring no more than 320 nanometers in diameter. A strand of human hair is roughly 100,000 nanometers thick.

Studying the process of balloon weaving is difficult due to the minuscule scales at which the action happens.

“Currently there are only a few studies which have researched the behavior of flying spiders,” Moonsung Cho, doctoral student at TU Berlin’s Institute of Biology, said in a news release. “The phenomenon is particularly common among young spiders. Some species suddenly fire threads into the air and only a light wind is required to carry them to heights of up to 4,500 meters and for distances of several hundred kilometers.”

Cho said he first became interested in the spiders’ flight capabilities after watching several specimens take to the air while taking a walk in the park. He was surprised to find the spiders take a detailed and deliberate approach to takeoff.

“Directly before taking off, they stretched out one of their legs in order to test the wind speeds,” Cho said. “I was fascinated by this at once.”

To better understand the phenomenon, Cho exposed crab spiders to different wind conditions in the lab. His experiments revealed new insights into the arachnids’ flying abilities. He found small spiders need only a few threads to take off, while larger specimens need 50 to 60 threads.

In the lab, the crab spiders only took to the air when winds were slower than three meters per second. Greater levels of turbulence allowed spiders to remain suspended in the air for longer.

Cho hopes his ongoing investigation of crab spider flight will eventually offer practical applications.

“It may be possible to examine whether passive flying structures inspired by the phenomenon of thread gliding can be used to explore dangerous weather conditions such as tornadoes or clear-air turbulence,” Cho said. “These are just considerations for now.”

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